The invention relates to improvements in spontaneous-combustion engines, especially to improvements in the pistons and cylinders of such engines. More particularly, the invention relates to improvements in engines (such as diesel engines) of the type wherein the combustion chamber is provided in the end face of the head or crown of the piston which reciprocates in the barrel of a cylinder and receives fuel and air through the head of the cylinder. Still more particularly, the invention relates to improvements in engines wherein the combustion chamber in the end face of the piston is surrounded by an annular groove or recess.
It is already known to provide the end face of the cylinder in a diesel engine with a recess which surrounds and communicates with the combustion chamber. Reference may be had, for example, to German Auslegeschrift No. 11 08 001 wherein the combustion chamber has a circular outline and the cylinder head has means for injecting fuel in such a way that the injected fuel impinges upon the surface surrounding the combustion chamber in close proximity to the open end of the chamber, i.e., at the end face of the piston crown. The purpose of the recess around the combustion chamber is to collect droplets of fuel which impinge upon and rebound from the surface surrounding the combustion chamber proper. The Auslegeschrift points out that spraying of fuel onto a hot surface results in quieter operation of the engine and reduces the fuel-sensitivity of the engine. The spray or sprays of fuel are to be injected in such a way that they contact the hottest portion of the surface bounding the combustion chamber, i.e., adjacent the end face of the crown. The depth of the recess is selected with a view to ensure that particles of fuel which rebound from the surface surrounding the combustion chamber are gathered in the recess instead of being propelled beyond the end face of the crown.
FIG. 1 of German Offenlegungsschrift No. 34 27 065 discloses a different piston whose end face is also formed with a combustion chamber and which has a chamfered surface surrounding the open end of the chamber. The reference does not point out the reasons and/or advantages of such configuration of the surface bounding the outermost portion of the combustion chamber. The reference also fails to disclose or suggest the optimum dimensions of the space within the chamfered portion of the surface.
German Offenlegungsschrift No. 33 43 677 discloses an engine for spontaneous combustion of liquid fuels wherein the end face of the piston is again provided with a circular combustion chamber. When the piston reaches the upper end of its stroke, the entire supply of admitted fuel and air is confined in the chamber. The admitted air is caused to circulate and causes circulation of fuel which is injected by a nozzle whose axis is inclined with reference to the axis of the piston. This induces the centrifugal force acting upon the contents of the combustion chamber to force the heavier cold air toward the surface bounding the chamber and to force the hot mixture of fuel and air toward the center of the chamber. In order to avoid the presence of pronounced edges which could interfere with the circulation of air and fuel in the combustion chamber, the conventional space for the tip of the fuel injection nozzle is replaced with a chamfered surface which is formed in a milling or like machine. This reference further proposes to provide the chamfered surface with a large outer diameter because this is supposed to ensure that the combustion products encounter little resistance during flow from the combustion chamber into the interior of the cylinder.